Using Path Difference in a Two Source Interference Pattern to Find the Wavelength of a Source

We can find the wavelength and frequency of waves using the interference pattern and path differences.
The diagram below shows two loudspeakers A and B a distance 0.8 m apart producing coherent sound of the same frequency and wavelength. 2 m away from the line joining the loudspeakers is parallel line along which a detector C is moved. When ABC form a right angle constructive interference occurs and the path difference between AC and BC is one wavelength.